Other Ab Flashcards
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Fluoroquinolones: Drugs
Ciprofloxacin, ofloxacin; respiratory fluoroquinolones: levofloxacin, moxifloxacin.
Fluoroquinolones: Mechanism
Inhibit prokaryotic topoisomerase II (DNA gyrase) and topoisomerase IV. Bactericidal. Oral absorption is markedly decreased by concurrent ingestion of divalent cations (e.g., dairy, antacids).
Fluoroquinolones: Clinical Use
Effective against gram ⊝ rods of urinary and GI tracts (including Pseudomonas), some gram ⊕ organisms, otitis externa, and community-acquired pneumonia.
Fluoroquinolones: Adverse Effects
- GI upset, superinfections, skin rashes, headache, dizziness.
- Less commonly: leg cramps, myalgias.
- Tendonitis or tendon rupture (especially in patients > 60 years old or on prednisone).
- Contraindicated in pregnancy, breastfeeding, and in children < 18 years old due to possible cartilage damage.
- May prolong QT interval.
Mnemonic: ‘Fluoroquinolones hurt attachments to your bones.’
Fluoroquinolones: Mechanism of Resistance
- Chromosome-encoded mutation in DNA gyrase.
- Plasmid-mediated resistance.
- Efflux pumps.
Daptomycin: Mechanism
Lipopeptide that disrupts gram ⊕ bacterial cell membranes by creating transmembrane channels.
Daptomycin: Clinical Use
Effective against S aureus skin infections (especially MRSA), bacteremia, infective endocarditis, and VRE.
Daptomycin: Adverse Effects
- Myopathy.
- Rhabdomyolysis.
Note: Not used for pneumonia (inactivated by surfactant). Mnemonic: ‘Dapto-myo-skin’—used for skin infections but can cause myopathy.
Metronidazole: Mechanism
Forms toxic free radical metabolites in bacterial cells, damaging DNA. Bactericidal and antiprotozoal.
Metronidazole: Clinical Use
Treats:
- Giardia.
- Entamoeba.
- Trichomonas.
- Gardnerella vaginalis.
- Anaerobes (Bacteroides, C difficile).
- Can replace amoxicillin in H pylori ‘triple therapy’ for penicillin-allergic patients.
Mnemonic: ‘GET GAP on the Metro’—treats anaerobic infections below the diaphragm (vs clindamycin for above diaphragm).
Metronidazole: Adverse Effects
- Disulfiram-like reaction with alcohol (flushing, tachycardia, hypotension).
- Headache.
- Metallic taste.
- Can cause tendonitis or tendon rupture in patients > 60 years old or on prednisone.
Note: Ciprofloxacin inhibits cytochrome P-450.
Linezolid: Mechanism
Inhibits protein synthesis by binding to the 23S rRNA of the 50S ribosomal subunit, preventing the formation of the initiation complex.
Linezolid: Clinical Use
Effective against gram ⊕ species, including MRSA and VRE.
Linezolid: Adverse Effects
- Myelosuppression (especially thrombocytopenia).
- Peripheral neuropathy.
- Serotonin syndrome (due to partial MAO inhibition).
Linezolid: Mechanism of Resistance
Point mutation of ribosomal RNA.
Macrolides: Drugs
Azithromycin, clarithromycin, erythromycin.
Macrolides: Mechanism
Inhibit protein synthesis by blocking translocation (‘macroslides’); bind to the 50S ribosomal subunit. Bacteriostatic.
Macrolides: Clinical Use
Used for atypical pneumonias (Mycoplasma, Chlamydia, Legionella), STIs (Chlamydia), gram ⊕ cocci (streptococcal infections in penicillin-allergic patients), and B pertussis.
Macrolides: Adverse Effects
MACRO:
- Gastrointestinal Motility issues.
- Arrhythmia due to prolonged QT interval.
- Acute cholestatic hepatitis.
- Rash.
- Eosinophilia.
- Increases serum levels of theophylline and oral anticoagulants. Clarithromycin and erythromycin inhibit cytochrome P-450.
Macrolides: Mechanism of Resistance
Methylation of the 23S rRNA-binding site prevents drug binding.
Polymyxins: Drugs
Colistin (polymyxin E), polymyxin B.
Polymyxins: Mechanism
Cationic polypeptides that bind to phospholipids on the cell membrane of gram ⊝ bacteria, disrupting cell membrane integrity, causing leakage of cellular components, and cell death.
Polymyxins: Clinical Use
Used as salvage therapy for multidrug-resistant gram ⊝ bacteria (e.g., P aeruginosa, E coli, K pneumoniae). Polymyxin B is a component of triple antibiotic ointments for superficial skin infections.
Polymyxins: Adverse Effects
- Nephrotoxicity.
- Neurotoxicity (e.g., slurred speech, weakness, paresthesias).
- Respiratory failure.
Sulfonamides: Drugs
Sulfamethoxazole (SMX), sulfisoxazole, sulfadiazine.
Sulfonamides: Mechanism
Inhibit dihydropteroate synthase, thereby inhibiting folate synthesis. Bacteriostatic (bactericidal when combined with trimethoprim).
Sulfonamides: Clinical Use
Effective against gram ⊕, gram ⊝, and Nocardia. TMP-SMX is used for simple UTIs.
Sulfonamides: Adverse Effects
- Stevens-Johnson syndrome.
- Urticaria.
- Liver damage.
- Folate deficiency.
- Optic neuritis.
- Nephrotoxicity.
- Agranulocytosis.
- Hemolysis if G6PD deficient.
- Kernicterus in infants.
Sulfonamides: Mechanism of Resistance
Resistance occurs through altered enzyme (dihydropteroate synthase), reduced uptake, or increased PABA synthesis.
Dapsone: Mechanism
Similar to sulfonamides but structurally distinct. Inhibits dihydropteroate synthase.
Dapsone: Clinical Use
Used for leprosy (both lepromatous and tuberculoid forms) and as prophylaxis or treatment for Pneumocystis jirovecii when combined with TMP.
Dapsone: Adverse Effects
- Hemolysis if G6PD deficient.
- Methemoglobinemia.
- Agranulocytosis.
Trimethoprim: Mechanism
Inhibits bacterial dihydrofolate reductase, making it bacteriostatic.
Cephalosporins: Mechanism
β-lactam drugs that inhibit cell wall synthesis but are less susceptible to penicillinases. Bactericidal.
Cephalosporins: Clinical Use (1st Generation)
1st generation (cefazolin, cephalexin)—gram ⊕ cocci, Proteus mirabilis, E coli, Klebsiella pneumoniae. Cefazolin is used prior to surgery to prevent S aureus wound infections.
Mnemonic: ⊕ PEcK.
Cephalosporins: Clinical Use (2nd Generation)
2nd generation (cefaclor, cefoxitin, cefuroxime, cefotetan)—gram ⊕ cocci, H influenzae, Enterobacter aerogenes, Neisseria spp., Serratia marcescens, Proteus mirabilis, E coli, Klebsiella pneumoniae.
Mnemonic: ⊕ HENS PEcK (2nd graders wear fake fox fur to tea parties).
Cephalosporins: Clinical Use (3rd Generation)
3rd generation (ceftriaxone, cefpodoxime, ceftazidime, cefixime)—serious gram ⊝ infections resistant to other β-lactams. Ceftriaxone is used for meningitis, gonorrhea, and disseminated Lyme disease. Ceftazidime for Pseudomonas.
Cephalosporins: Clinical Use (4th Generation)
4th generation (cefepime)—effective against gram ⊝ organisms, with enhanced activity against Pseudomonas and gram ⊕ organisms.
Cephalosporins: Clinical Use (5th Generation)
5th generation (ceftaroline)—broad coverage of gram ⊕ and gram ⊝ organisms. Unlike earlier generations, covers MRSA and Enterococcus faecalis but not Pseudomonas.
Cephalosporins: Adverse Effects
- Hypersensitivity reactions.
- Autoimmune hemolytic anemia.
- Disulfiram-like reaction.
- Vitamin K deficiency.
- Low cross-reactivity in penicillin-allergic patients.
- Enhanced nephrotoxicity with aminoglycosides.
Cephalosporins: Mechanism of Resistance
- Inactivated by cephalosporinases (a type of β-lactamase).
- Structural changes in penicillin-binding proteins (PBPs).
Cephalosporins: Key Limitations
Organisms not covered by 1st–4th generation cephalosporins: LAME
- Listeria
- Atypicals (Chlamydia, Mycoplasma)
- MRSA
- Enterococci.
β-lactamase Inhibitors: Drugs
Clavulanic acid, Avibactam, Sulbactam, Tazobactam.
β-lactamase Inhibitors: Use
Added to penicillins to protect them from β-lactamase destruction.
Examples: amoxicillin-clavulanate, ceftazidime-avibactam, ampicillin-sulbactam, piperacillin-tazobactam (CAST).
Carbapenems: Drugs
Imipenem, meropenem, ertapenem.
Carbapenems: Mechanism
Broad-spectrum β-lactamase-resistant antibiotics. Bind penicillin-binding proteins, inhibiting cell wall synthesis and causing bacterial cell death.
Carbapenems: Clinical Use
Effective against gram ⊕ cocci, gram ⊝ rods, and anaerobes. Reserved for life-threatening infections or when other drugs fail.
Imipenem is co-administered with cilastatin to prevent renal inactivation (‘the kill is lastin’ with cilastatin’).
Ertapenem lacks activity against Pseudomonas.
Carbapenems: Adverse Effects
- GI distress.
- Rash.
- CNS toxicity (seizures) at high plasma levels.
Carbapenems: Mechanism of Resistance
Inactivation by carbapenemases produced by organisms such as K pneumoniae, E coli, and Enterobacter spp.
Aztreonam: Mechanism
Prevents peptidoglycan cross-linking by binding penicillin-binding protein 3. Resistant to β-lactamases. Synergistic with aminoglycosides.
Aztreonam: Clinical Use
Effective against gram ⊝ rods only. No activity against gram ⊕ rods or anaerobes. Used for penicillin-allergic patients and those with renal insufficiency who cannot tolerate aminoglycosides.
Aztreonam: Adverse Effects
Usually well-tolerated but may cause occasional GI upset.
Vancomycin: Mechanism
Inhibits peptidoglycan synthesis by binding D-Ala-D-Ala of cell wall precursors. Bactericidal (bacteriostatic for C difficile). Not susceptible to β-lactamases.
Vancomycin: Clinical Use
Effective against gram ⊕ organisms, including MRSA, S epidermidis, Enterococcus species, and Clostridium difficile (oral route).
Vancomycin: Adverse Effects
- Red man syndrome (histamine-mediated flushing).
- Nephrotoxicity.
- Ototoxicity.
- Thrombophlebitis.